1. Field of the Invention
The present invention relates to a method of manufacturing an electron device such as a semiconductor device, a superconductive device, a micro machine and an electronic device, a pattern forming method used for the method, a photomask used for these methods and its manufacturing method, particularly relates to technique effective to apply to exposure technology in a process for manufacturing a semiconductor integrated circuit.
2. Description of the Related Prior Arts
In manufacturing a semiconductor integrated circuit, for a method of printing a minute pattern on a semiconductor wafer, lithography is used. In lithography, a projection tool is mainly used, a pattern of a photomask installed in a projection tool is printed on a semiconductor wafer and a device pattern is formed.
A normal photomask is produced by processing light shielding materials such as chromium (Cr) formed on the flat surface of a transparent quartz substrate. That is, a light shielding film made of chromium or others is formed on the flat surface of a quartz substrate in a desired shape. For the processing of the light shielding film, for example, after an electron beam sensitive resist is applied on the light shielding film, a desired pattern is written on the electron beam sensitive resist by an electron beam writer, next, a resist pattern in a desired shape is formed by development, afterward, dry etching or wet etching is applied using the resist pattern as a mask and the light shielding film is processed. Afterward, after the resist is removed, cleaning and others are performed and a light shielding pattern in a desired shape is formed on the transparent quartz substrate.
Recently, the integration of LSI has been accelerated, the enhancement of the operational speed has been demanded and the miniaturization of a circuit pattern has been demanded. This tendency particularly remarkably appears in a gate pattern that has a large effect upon the operational speed of a transistor. For a part of logic LSI products, a gate pattern of 0.1 xcexcm is also already formed using a KrF excimer laser (wavelength: 248 nm) for exposure.
For a semiconductor memory, miniaturization is accelerated to reduce the cost and a dynamic random access memory (DRAM) according to a rule that half pitch is 0.18 xcexcm is manufactured using a KrF excimer laser for exposure. DRAM according to a rule that half pitch is 0.13 xcexcm using a KrF scanner is also developed.
It is owing to an exposure method called super resolution that by far smaller patterning than the wavelength of exposure is enabled. Super resolution effective to form a minute pattern is called phase shift lithography and is disclosed in Japanese published unexamined patent application No. Sho 58-173744 for example. The phase shift lithography is a method of forming structure called a phase shifter for alternately inverting the phase of exposure light in windows in which a part where exposure light is transmitted of a photomask, that is, a glass face is seen with a light shielding part between the windows and exposing using this photomask. As the phase of light transmitted in both transmitted parts is inverse, the amplitude of light may be zero in the light shielding part between the parts. In case the amplitude is zero, the intensity of light is also zero and the resolution is greatly enhanced.
For an example of the disclosure of another technique related to a mask, Japanese published unexamined patent applications No. Hei 9-211837 and No. Hei 5-289307 can be given.
For a phase shifter, there are a carved type that a part of a glass plate as a photomask is carved, a type that a transparent film having the thickness enough to invert the phase is formed on the base material of a photomask and a type that these two are mixed.
A carved type phase shift mask is produced as follows. As shown in (a) of FIG. 2A, a Cr film 202 made of light shielding material is deposited on the flat surface of mask base material (a quartz substrate) 201 by sputtering and an EB resist 203 is applied to it. A pattern for light shielding is written by EB (shown by an arrow 204). The pattern is developed, a resist pattern 205 is formed ((b) of FIG. 2A), the Cr film 202 is etched by dry etching or wet etching ((c) of FIG. 2A), the resist is removed and a light shielding pattern 206 is formed C(d) of FIG. 2A). Afterward, an EB resist 207 is applied and a pattern for forming a phase shifter is exposed (shown by an arrow 208)((e) of FIG. 2A). Development is performed, a resist pattern 209 is formed ((f) in FIG. 2B) and the quartz substrate is carved by desired depth by dry etching ((g) of FIG. 2B). The resist is peeled, phase difference between both apertures 210 and 211 is inspected ((h) of FIG. 2B), in case carved quantity for making phase difference does not reach a target value, an EB resist 212 is applied again, a shifter pattern is written 213 ((i) in FIG. 2B), development is performed, a shifter pattern 214 is formed ((j) in FIG. 2B), the quartz substrate is etched again by dry-etching ((k) in FIG. 2C), the resist is peeled and phase difference is inspected ((l) in FIG. 2C). Afterward, as shown in (m) of FIG. 2C, wet etching is performed, overhang structure 215 having the Cr film as an overhang is formed and a carved type phase shift mask is manufactured.
In the meantime, a transparent film formation type (hereinafter called an additive phase shifter type) phase shift mask is produced as follows. As shown in (a) of FIG. 3A, a Cr film 302 made of light shielding material is deposited on the flat surface of a mask substrate (a quartz substrate) 301 by sputtering and an EB resist 303 is applied on it. A pattern for light shielding is written by EB (304). Development is performed, a resist pattern 305 is formed ((b) of FIG. 3A), the Cr film is etched by dry etching or wet etching ((c) of FIG. 3A), the resist is removed and a light shielding pattern 306 is formed ((d) of FIG. 3A).
Afterward, a spin-on-glass (SOG) film is applied, heating processing and others are performed and a transparent shifter 307 is formed ((e) in FIG. 3A). Afterward, an EB resist 308 is applied and a pattern for forming a phase shifter is exposed (309) ((f) in FIG. 3B). Development is performed, a resist pattern 310 is formed ((g) in FIG. 3B) and a transparent shifter is etched by dry etching or wet etching ((h) in FIG. 3B). The resist is peeled, phase difference between both apertures 311 and 312 is inspected and a phase shift mask is acquired ((i) in FIG. 3B).
For light shielding material in both methods, the metallic Cr film is used and in addition, as the accuracy of the light shielding pattern is required, the metallic Cr film is formed on the flat surface of the quartz substrate by sputtering.
For the type of the phase shift mask, there are a shifter edge type that phase difference is given to the light shielding pattern 401 which can be regarded as an optically isolated pattern as shown in FIG. 4 by optical path difference 402 on both sides of the light shielding material 401 and Levenson type that a phase shifter 502 is alternately arranged on a light shielding pattern 501 closely assembled like a line and space as shown in FIG. 5 in an aperture. Reference numbers 403 and 503 in FIGS. 4 and 5 both denote a glass substrate. In both cases, structure for inverting the phase of exposure light transmitted in the aperture on both sides of the aperture is also provided.
A problem in the printing characteristics of the carved type phase shift mask is that the quantity of transmitted light in an aperture 602 (hereinafter called a phase 0) in which a glass substrate 601 is not carved or is not carved so much as shown in (a) of FIG. 6 and in an aperture 603 (hereinafter called a phase xcfx80) in which the glass substrate is deep carved varies by light scattering on the side 605 of the glass substrate formed under the side wall 604 of Cr light shielding material and the dimension difference of a pattern called 0/xcfx80 difference is caused by the variation.
To prevent this, a side etch carved type that the glass side 611 is backed from the edge 612 of Cr light shielding material 613 as shown in (b) of FIG. 6 and light scattered on the glass side is shielded by the Cr light shielding material is proposed.
However, in this case, there is a problem that the width 614 of glass supporting the Cr light shielding material 613 is thinned as the pattern is miniaturized and miniaturization is impossible in view of the strength. Particularly, in a both sides carved type of mask in which the glass substrate 601 is also carved in the phase 0 602 as shown in (c) of FIG. 6, the problem of area in which the Cr film and the glass are touched is a large problem. The Cr light shielding material 613 is required to be supported by a thin glass support 616 and as a pattern becomes complex and minute, the problem becomes more serious.
Further, recently, the magnification of a mask of a lithography equipment progresses from xe2x80x9c10xc3x97xe2x80x9d to xe2x80x9c5xc3x97xe2x80x9d and further, to xe2x80x9c4xc3x97xe2x80x9d, hereby, as a dimension on the mask is required to be further acceleratedly reduced by the reduction of a device dimension, the thinness of the support is a definite problem that determines the limit of printing. In manufacture, there is a problem that foreign matters accumulate in a pocket 615 and the yield of masks is hardly enhanced. When the shifter is carved by dry etching, there is a problem that carved depth differs depending upon a pattern dimension by micro loading effect in etching and therefore, a phase angle differs according to the pattern dimension. Further, As shown in FIGS. 2A to 2C, there is a problem that as the number of mask manufacturing processes is many, a mask manufacturing cost is high, time required for manufacture is long, turn around time (TAT) is large and the number of processes is many, the yield is low.
In the meantime, in the additive phase shifter type phase shift mask, as shown in FIG. 5, there is a problem that as the shifter 502 is formed on the Cr light shielding film 501 made of light shielding material, the phase shifter cannot be formed with fixed thickness, the phase angle varies according to a pattern dimension and the phase (that is, the thickness of the shifter) varies between the center 504 of the pattern and the periphery 505 in one pattern.
Furthermore, even if a phase shifter is produced beforehand and the formation on the phase shifter of a Cr light shielding film is tried to solve the problems, it is extremely difficult to form a Cr film free of a defect and having high quality by sputtering on a substrate having difference in a level because of the shifter. Further, there is a problem that as the Cr film made of light shielding material is formed on the shifter, the surface of the Cr film is not flat, the Cr film has inclined or irregular structure, exposure light is largely reflected and a pattern printing characteristic is deteriorated. For example, as shown in FIG. 16, it is proposed that a countermeasure for forming a Cr oxide layer 1404 for preventing reflection on the surface of a Cr film 1403 formed on blanks 1401 made of a quartz transparent substrate and preventing reflection from the surface of the Cr film using a thin film interference phenomenon is taken, however, there is an extremely important problem in accelerating a minute pattern that as a part of the Cr film covers a shifter pattern 1402, the Cr film has an inclined or irregular surface, a diagonal part 1405 is partially formed, as the thickness of the Cr oxide film there cannot be precisely controlled according to a predetermined reflection prevention condition, the reflectivity partially differs as shown by arrows 1406 and 1407 in FIG. 16 and a printing characteristic is deteriorated.
Therefore, it has been more and more difficult to manufacture the electron device provided with the complex and minute patterns using such a mask and a projection tool precisely and with a high yield.
Therefore, the object of the invention is to provide the improved manufacturing method of an electron device using a phase shift mask. For example, the object is to provide a method of manufacturing an electron device formed by plural minute patterns having the width and an interval of 0.1 xcexcm or less using a projection tool and phase shift mask technique with a satisfactory yield.
Another object of the invention is to provide a minute pattern forming method suitable for the manufacturing method of such an electron device and a mask improved for the method.
Further another object of the invention is to provide improved technique that can enhance the critical dimension accuracy of lithography equipment in a method of manufacturing an electron device using a phase shift mask.
Further concretely, the object is to provide a minute pattern forming method wherein no dimension accuracy is deteriorated by the effect of reflected light from the surface of light shielding material in projection exposure using a phase shift mask having high phase angle controllability and others and provide a minute electron device using the method.
The outline of the representatives of the inventions disclosed in this application will be briefly described below.
That is, in the invention, a phase shifter having predetermined thickness is partially formed on the flat surface of a transparent plate, a light shielding pattern is printed on a photosensitive film provided on the surface of a workpiece using a mask where a light shielding film that covers the end of the shifter, is made of non-metal and has a predetermined pattern is partially provided by a projection tool and an electron device is manufactured by developing the photosensitive film. Further concretely, the pattern is printed by projection exposure using a mask where the light shielding film made of non-metal is partially extended on the surface of the shifter and the transparent plate including the end of the shifter.
In another invention, a concavity or a convexity having predetermined depth or height is partially formed on the flat surface of a transparent plate, a light shielding pattern is printed on a photosensitive film provided on the surface of a workpiece using a mask wherein a light shielding film that covers the end of the concavity or the convexity, is made of non-metal and has a predetermined pattern is partially provided by a projection tool and an electron device is manufactured by developing the photosensitive film. Further concretely, the pattern is printed by projection exposure using a mask where the light shielding film made of non-metal is partially extended on the surface including the end of the concavity or the convexity of the transparent plate and adjacent to the end of the concavity or the convexity of the transparent plate by projection exposure.
In any invention, as phase shift means is formed on the flat surface of the transparent plate, the phase shift angle of exposure light in the phase shifter in printing can be secured in a predetermined region precisely.
In any invention, for a light shielding film made of non-metal, a light shielding film the reflectivity of exposure light in printing of which is smaller than that on a metallic film such as a Cr film is desirable and it is desirable that for example, a film made of dielectric material, high resistance material or organic material is used. Further concretely, it is also favorable to manufacture the mask itself that the light shielding film itself is a photosensitive film and it is desirable that a photoresist made of novolac resin or phenol resin is used. Or it is desirable that a photosensitive film such as a polyaniline resin film is used.
As the reflectivity of exposure light in printing can be made smaller than that on a metallic film such as a Cr film from relation with the refractive index by using a film made of dielectric material, high resistance material and organic material for a light shielding film, a flare can be reduced even if the light shielding film has the irregular surface and the invention is advantageous to enhance the resolution and the dimension accuracy. As described later, as waveguide effect caused on the side wall due to the thickness of the light shielding film (that is, a mask pattern) itself can be reduced by exposure light in printing, difference in a dimension after processing made by the difference in the thickness of the light shielding film can be reduced even if the light shielding film has the irregular surface and the invention is extremely advantageous to enhance processing accuracy.
As described above, according to the invention, as a phase shift angle in a mask can be precisely controlled, and the resolution and the dimension accuracy in printing can be enhanced, the manufacturing yield of an electron device such as a semiconductor integrated circuit provided with a complex and minute pattern can be enhanced.
(a) in FIG. 1 shows an example of a mask according to the invention. As clear from FIG. 1, the mask has an undernearth phase shifter additive light shielding mask structure in which a light shielding pattern 3 made of dielectric material, high resistance material or organic material is formed at the end of the phase shifter 2 so that the light shielding pattern covers a part having difference in a level formed by the surface of the phase shifter and the surface of the blanks 1 after a transparent phase shifter 2 patterned on the flat surface of blanks 1 such as a transparent quartz plate is formed beforehand. When a mask manufacturing process is considered, a case that the light shielding pattern is written on the upside as shown in FIG. 1 is easily understood, however, when a mask is inserted into lithography equipment in printing, the mask is installed in the lithography equipment in a direction shown in (b) FIG. 1, that is, in a state in which the pattern face of the mask is opposite to the surface of a workpiece 11 to be an electron device of a semiconductor substrate and others on the surface of which a photosensitive photoresist film 12 is provided, projected exposure light 15 is radiated from the top, that is, from the rear surface of transparent blanks and the photosensitive film 12 on the surface of the workpiece 11 is exposed according to a mask pattern formed by the light shielding material 3. The light shielding pattern is printed on the photosensitive film by developing the exposed photosensitive film 12.
Further, if a transparent film (not shown in FIG. 1) the refractive index nxe2x80x2 of exposure light having the wavelength of xcex in printing of which is larger than the refractive index of the blanks glass and is smaller than the refractive index n of the phase shifter is provided between the phase shifter 2 and the mask substrate (so-called blanks glass) 1 so that the following expression is met (the thickness of the transparent film: dxe2x80x2), dimension accuracy is further enhanced.
sin(2xcfx80nxe2x80x2(dxe2x80x2+xcex/2(nxe2x88x921))/xcex)=sin(2xcfx80nxe2x80x2dxe2x80x2/xcex) 
Also, when the section in the direction of the thickness of the end of the phase shifter 2 is an inclined shape (that is, a tapered shape), the dimension accuracy of the light shielding pattern formed on the phase shifter is enhanced and bonding strength is enhanced, however, as occupied area is increased by the quantity, it is desirable that the taped angle is 45 degrees or more. Actually, approximately 60 degrees is desirable.
Furthermore, if the phase shifter 2 is formed using photosensitive SOG, the mask manufacturing process can be greatly reduced, TAT is also enhanced and further, the yield of the mask is also enhanced.
Further, in case the light shielding pattern 3 in the phase shift mask was formed by a photoresist film, these inventors found that there were the following various problems when a photomask was actually used in the manufacturing process of a semiconductor integrated circuit and in the actual manufacture of the phase shift mask and found their solving means.
First, the detection of a pattern depending upon a so-called alignment mask between the shifter and the light shielding material and a pattern measurement mark for relatively positioning a shifter pattern of the phase shift mask and the light shielding pattern is difficult. This comes into question particularly in case the phase shifter is formed beforehand. The shifter has a type in which the glass substrate is carved and a type in which SOG and others are deposited, and the material is the same or the similar as/to the material of the glass substrate. Therefore, difference between an electron beam for writing used in alignment and the reflectivity at the edge of the mark of the shifter is small and the detection of a pattern is difficult. Therefore, in case a shifter pattern is formed beforehand, it is difficult to align the shifter pattern and the light shielding pattern. Its solving means is as follows.
Before the shifter is formed, a metal region made of metal is arranged outside a pattern region to be printed on the surface of the mask substrate, that is, outside an integrated circuit pattern formation region in the manufacture of a semiconductor integrated circuit and an alignment mark to be an alignment criterion when a shift pattern and a light shielding pattern are written is formed on the metal. A first problem is solved by this means.
Second, it is difficult to detect a predetermined pattern used for detecting various information such as a device discrimination mark. For example, in a mask inspection machine, a tungsten halogen lamp and others are mainly used for the alignment of a mask, however, as transmissivity in a resist is high and a high contrast cannot be acquired when a detection mark on a mask is formed by a resist pattern in case the mask is installed in a mask inspection machine, it is difficult to detect a pattern. Therefore, it is difficult to align the mask and the inspection machine and there is a problem that satisfactory inspection is impossible. Not only when a mask is installed in the inspection machine but when a mask is installed in lithography equipment, a mark for identifying the form of a mask is required. At this time, it is desirable to enhance work efficiency that a mark which an operator can read is also provided in addition to a mark read by a machine. At this time, a character directly written on the glass substrate with the shifter and resist light shielding material is very difficult to read and an error in reading occurs. Its solving means is as follows.
A metal region made of metal is arranged on the mask substrate outside a pattern region to be printed, that is, outside an integrated circuit pattern formation region in a method of manufacturing a semiconductor integrated circuit, a criterion mark for aligning with an inspection machine and a mark pattern such as a character and a symbol for identifying a mask are formed on the metal. At this time, an aperture is formed on the metal, can be also used for a criterion mark and an identification symbol, a metal plate is formed, a pattern is formed with the shifter and a resist on the metal plate and can be also used for a criterion mark and an identification pattern. A second problem is solved by this means.
Third, a problem that a foreign matter is caused when a mask is installed in an inspection machine, lithography equipment and others occurs. In the technique described above, as a resist of a mask is directly touched to a mask fixing member (for example, a vacuum chuck) of an inspection machine, lithography equipment and others when the mask is installed the inspection machine, the lithography equipment and others and is carried, a foreign matter is caused because the resist chips or is chipped. There is a problem that as this foreign matter adheres to the surface of a lens of the inspection machine and the lithography equipment, contaminates a chamber and adheres to the surface of a semiconductor wafer for example, the inspection accuracy and the dimension accuracy of a pattern are deteriorated and as failure such as the short circuit of a pattern and the failure of an open circuit occur, the reliability and the manufacturing yield of a semiconductor device are deteriorated.
To solve this problem, these inventors proposed that when a photomask was installed in predetermined equipment such as the inspection machine and the lithography equipment and was carried, a photomask in which a light shielding pattern was arranged on the principal surface in the center of a mask substrate was used so that the light shielding pattern made of a resist on the mask substrate of the photomask and an installing part of the predetermined equipment are not touched. These inventors also proposed that when a photomask was installed in predetermined equipment, predetermined processing was executed in a state in which an installing part of the predetermined equipment was touched to a region (that is, the periphery) in which no light shielding pattern made of a resist exists on the principal surface of a mask substrate of the photomask. The third problem is solved by these means.